Getting the Heat Right in Long Glass Tunnel Kilns
If you’re heating glass for molding in a tunnel kiln, you know the struggle. You need a thermal profile that doesn’t budge. But once your tunnels stretch past two meters, the standard lamps you buy off the shelf just aren’t enough. That’s why we build custom, continuous infrared units. The goal is simple: kill the cold spots. Because when you have a cold spot, you get glass stress. And when you have stress, you have ruined parts. Dealing with length and power Building a heating unit longer than two meters is a bit of a balancing act. You’ve got to worry about voltage drops and the fact that materials expand when they get hot. We handle this by building continuous arrays or specialized long-tube units. It keeps the heat density steady across the whole footprint. We tweak the filament winding and voltage so you get the same wattage per centimeter from start to finish. One heads-up: if you’re pushing high wattage into one long tube, make sure your power supply can take the hit. That initial cold-start current spike can trip breakers if you aren’t prepared for it. The gear we use We stick with high-purity quartz glass for the filaments. For glass molding, shortwave infrared is the way to go—it sinks into the material much faster than longwave. It’s snappy. It reacts quickly. And since kilns can vibrate, we use heavy-duty connectors. Nobody wants to be hunting for a loose lamp in the middle of a production run. Killing the “Cold Spot” headache The biggest pain in the neck with tunnel kilns is the gap between the lamps. That little bit of space is where the trouble starts. We solve this by overlapping the radiation patterns in a continuous layout. The glass never gets a chance to cool down as it moves from one zone to the next. It just stays hot. But here’s the thing: you have to be careful with the mounting brackets. Quartz expands when it hits operating temperature. If your mounts are too tight, the tubes will just snap. We build in a “floating margin” so the quartz can breathe. And don’t forget your cooling system. If it isn’t spec’d to handle the ambient heat buildup inside the housing, you’re going to fry your wiring.